Internazionale clinched their 20th Serie A title by beating Milan in a feisty derby at San Siro, giving Simone Inzaghi’s side an unassailable lead in the standings. A goal from Francesco Acerbi and Marcus Thuram in each half proved sufficient to secure Inter’s victory, with Fikayo Tomori scoring late in the game to reduce the deficit.

The match also featured three red cards in stoppage time, with Milan being reduced to nine men as tensions flared. Theo Hernández and Davide Calabria got their marching orders along with Inter’s Denzel Dumfries.

Related: Internazionale beat Milan 2-1 to win Serie A title – live

Inter, who have lost only once in the league this season, hold a 17-point advantage over second-placed Milan with five matches remaining. The San Siro was packed with supporters from both clubs, with Inter fans displaying two stars to symbolise their impending 20th Scudetto, spelling out a message to their rivals: “Our destiny, your nightmare”.

The game heated up in the opening minutes as both sides engaged in pushing and shouting following a late challenge on Inter’s Nicolò Barella. However play resumed a few minutes later without any bookings.

The away fans erupted after 18 minutes when Benjamin Pavard flicked a corner to a completely unmarked Acerbi, who had little trouble heading Inter ahead. Four minutes after the break, Thuram doubled Inter’s lead by sending a low shot from the edge of the box into the bottom-left corner.

Milan reignited the match 10 minutes before full time when a save from the Inter goalkeeper Yann Sommer rebounded off a post and fell into the path of Tomori, who headed home.

In stoppage time, tempers flared as a scuffle broke out between the players which resulted in Dumfries and Hernández being shown red cards. Yet another brawl ensued on the pitch minutes later, culminating in Milan’s Calabria receiving a red card for striking Davide Frattesi.

“This is a wonderful, unforgettable evening,” Inzaghi said during the celebrations.

“It’s something to be shared with everyone in the world of Inter, from the club directors to our president.”